1. Field of the Invention
The present invention relates to a sensorless switched reluctance motor driving apparatus and method thereof which detects a position of a rotor with change of electric currents at each phase without installing a separate position detecting sensor, to thereby drive the motor.
2. Description of the Prior Art
In general, the sensorless switched reluctance motor (hereinafter referred to as a motor) is usually used for compressors which cannot be attached with a position sensor because of driving conditions such as temperature, humidity, repair and maintenance cost and the like.
The motor, as shown in FIGS. 1, 2, 3 and 4, is disclosed at a Korean patent (No. 95-15171). FIGS. 1a and 1b are motor circuits in accordance with a first embodiment of the prior art. The conventional motor, as each phase thereof is magnetized at a predetermined sequential procedure, is provided with a motor driving unit 10, a high pass filter unit 20 having voltages (RCA), (RCB), (RCC) to detect currents at respective phases and high pass filters (20A-20C) which differentiate and amplify properly to measure the increase or decrease of the detected currents, a first amplifying unit (30) for amplifying the respective phase voltages (V1), (V2), (V3) output from the high pass filter unit 20 into the proper levels thereof, a first comparison unit 40 for outputting signals of over the reference voltage levels in comparing the voltages (VA), (VB), (VC) output at the first amplifying unit 30 with the predetermined reference voltage levels, a delay unit 50 for delaying respective phase voltages (V1), (V2), (V3) from the high pass filter unit 20 for a predetermined time duration, a second amplifying unit 60 for amplifying the voltages output from the delay unit 50 into proper levels thereof, a second comparison unit 70 for outputting signals of over the reference voltage levels in comparing the voltages (VA.sup.d), (VB.sup.d), (VC.sup.d) output at the second amplifying unit 60 with the predetermined reference voltage levels and an "OR gating" unit 80 for "OR gating" the phase voltages output from the first and second comparison units 40, 70.
Operational effects of the conventional motor thus constructed are described in detail with reference to FIGS. 2, 3 and 4. If predetermined gate signals are subsequently applied from a base driving unit (not shown) to Metal Oxide Semiconductor (MOS) transistors (M1, M2), (M3, M4), (M5, M6), an electric current is to flow through the transistors (M1, M2), (M3, M4), (M5, M6) to coils (La), (Lb), (Lc). Then, the inductance change at respective phases are generated according to the changing positions of the rotor 11 as shown in FIG. 3 at (A), (B) and (C), respectively.
At this time, as the rotor 11 is rotated as shown in FIG. 2, reverse electric motive force generated at a wiring of the stator 12 to flow the phase currents, shown at (A), (B), (C) in FIG. 4, to the phase current detecting resistances (RCA), (RCB)(RCC), where voltages of small value are used to reduce loss thereof in the resistances (RCA), (RCB), (RCC).
The currents (iA), (iB), (iC) detected by the phase current detecting resistances (RCA), (RCB), (RCC) are, in sequence, differentiated by the high pass filters (20A-20C) having condensers, resistances and operation amplifiers (CA, RA, OP1), (CB, RB, OP2), (CC, RC, OP3), supplied to respective amplifiers of the first amplifying unit 30 (AMP1), (AMP2), (AMP3), amplified them into proper levels thereof to form the wave forms of (D), (E), (F) in FIG. 4, and then compared with the reference voltages pre-set at comparing means (C71), (C72), (C73) to output only higher levels of voltages than the reference voltages (Vref1, Vref2, Vref3).
The voltages (-V1), (-V2), (-V3) output from the high pass filters (20A-20C) are turned in reverse and delayed for a predetermined time duration at delaying means (RD1, C D1), (R D2, C D2) (R D3, C D3). At this time, the delay signals thereof are amplified into proper levels thereof at the amplifiers (AMP4), (AMP5), (AMP6) of the second amplifying unit 60 to be transmitted as signals of (D), (E), (F) in FIG. 4.
The voltages (VA.sup.d), (VB.sup.d), (VC.sup.d) output from the amplifiers (AMP4), (AMP5), (AMP6) are compared with the predetermined reference voltages (Vref4, Vref5, Vref6) at comparing means (C74), (C75), (C76) to output only higher levels of voltages than the reference voltages (Vref4, Vref5, Vref6). Then, the voltages are ORed with the voltages output from the comparing means (C74), (C75), (C76) at the OR gates (OR1) (OR2), (OR3) to transmit the wave forms of (G), (H), (I) in FIG. 4, which are used for detecting the position of the rotor 11.
However, there is a problem in the conventional motor in that the position angles of the rotor are detected by characteristic features of the filter unit or the delay unit, thereby getting the position firing angles of the rotor to be changed in case of controlling variable speed thereof.
In addition, there is another problem in the conventional motor in that the high frequency of noise caused by the high pass characteristic feature of the filter unit influences on output thereof to generate a firing angle signal from the signal weak at noise, to thereby cause a possibility of stopping the motor due to the unfit firing angles thereof.
Furthermore, there is still another problem in that external mechanical noise is induced to change the current wave forms, to thereby cause a possibility of chattering phenomenon at the output thereof at the comparing means after being passed through the filter unit.